The present invention relates to a slide bearing for cooling water circulation pump employed in a fuel cell.
FIG. 1 shows a conventional electric water pump, which includes a housing 1, and a rotary shaft 3 having both ends thereof supported on the housing 1 through slide bearings 2 and 6. An impeller 4 is fixed to one end of the rotary shaft 3. A rotary member 5 is integrally formed on the rotary shaft 3. In order to activate the pump, i.e. to produce a water flow in the pump chamber as shown by arrows in FIG. 1, the rotary member 5 is driven by an electric motor to rotate the impeller 4.
In addition to the slide bearings 2 and 6, a mechanical seal (not shown) may also be mounted on the rotary shaft 3 of the water pump to seal the gap between the rotary shaft 3 and the slide bearing 6, thereby preventing entry of water or vapor into the drive unit such as an electric motor.
Some conventional water pumps for circulating cooling water for motor vehicle engines and other water pumps used in motor vehicles have their parts formed of a polyphenylene sulfide resin composition (see JP patent publication 6-116494).
JP patent publication 2002-139045 discloses a water pump for a motor vehicle in which its rotary shaft is supported on the housing through slide bearings made of a resin. In order that the slide bearings maintain high slidability, wear resistance and mechanical strength for a prolonged period of time even if the slide bearings are kept in contact with an anti freeze at a high or low temperature, the slide bearings are made of a polyetherketone resin.
If this type of conventional slide bearings for an automobile water pump are used as slide bearings for a cooling water circulation pump in a fuel cell, the performance of the fuel cell often declines.
This is because if such slide bearings are used in a fuel cell, impurities tend to mix into pure water used as a coolant in the fuel cell, thereby lowering the efficiency of the fuel cell and also shortening the life of the fuel cell. But the exact cause for the increase in impurities has not been known and therefore no concrete measures thereagainst have been established so far.
Since it was impossible to completely prevent mixing of impurities into the coolant because its cause is unknown, it was possible only to remove impurities with e.g. a water purifier.
An object of the present invention is to provide a slide bearing which will not cause impurities to be mixed into a coolant of a fuel cell when used in the fuel cell.